The invention relates to a self-starting permanent magnet synchronous motor, a compressor using the motor, and further, a refrigeration cycle using the motor.
Generally, according to an induction motor, since it has a rigid structure and a line-start can be performed by a commercially available power source, it has such an advantage that the induction motor can be constructed at low costs as a driving source of a machine of a constant speed driving which does not need speed control.
According to the self-starting permanent magnet synchronous motor, the line-start can be performed by the commercially available power source in a manner similar to the foregoing induction motor, a driving unit can be constructed without adding an inverter, and further, a secondary copper loss at the time of the stationary operation is very small. There is, consequently, such an advantage that it is possible to largely contribute to realization of a high efficiency of a driving system for the above induction motor.
As a disadvantage of the self-starting permanent magnet synchronous motor, a point that since permanent magnets are arranged on the inner rim side of a squirrel-cage winding, a magnetic flux axis of a rotor has already been fixed can be mentioned. That is, a starting torque which is caused in the rotor upon starting is a synthesized torque of both of an induction torque which is caused in the squirrel-cage winding and an attraction force of permanent magnet magnetic fluxes and a stator magnetic flux which is generated by applying a power source. According to the line-start by the commercially available power source, such a situation that a position of the rotor can be specified as in the case of driving the inverter cannot be realized (a voltage phase cannot be controlled). Therefore, in dependence on the phase of the voltage which is applied upon starting, there is a case where the magnet magnetic fluxes and the stator magnetic flux repel each other or a case where the magnets are attracted in the direction opposite to the normal rotating direction and a negative torque is generated. There is, consequently, such a problem that a large difference occurs in the torque at the time of starting due to the phase of the voltage which is applied, that is, the position where the stator magnetic flux is generated.
As a rotor of such a self-starting permanent magnet synchronous motor, for example, the rotors having various kinds of structures have already been known in JP-A-4-210758, JP-A-10-336927 and JP-A-2001-37126.